Fix strip_routing_prefix to handle kimi provider prefix (US-023)

Add "kimi" to the strip_routing_prefix matches so that models like
"kimi/kimi-k2.5" have their prefix stripped before sending to the
DashScope API (consistent with qwen/openai/xai/grok handling).

Also add unit test strip_routing_prefix_strips_kimi_provider_prefix.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Yeachan-Heo

rust/crates/api/src/providers/openai_compat.rs

@@ -801,7 +801,7 @@ fn strip_routing_prefix(model: &str) -> &str {
         let prefix = &model[..pos];
         // Only strip if the prefix before "/" is a known routing prefix,
         // not if "/" appears in the middle of the model name for other reasons.
-        if matches!(prefix, "openai" | "xai" | "grok" | "qwen") {
+        if matches!(prefix, "openai" | "xai" | "grok" | "qwen" | "kimi") {
             &model[pos + 1..]
         } else {
             model
@@ -2199,4 +2199,12 @@ mod tests {
         assert_eq!(OpenAiCompatConfig::openai().max_request_body_bytes, 104_857_600); // 100MB
         assert_eq!(OpenAiCompatConfig::xai().max_request_body_bytes, 52_428_800); // 50MB
     }
+
+    #[test]
+    fn strip_routing_prefix_strips_kimi_provider_prefix() {
+        // US-023: kimi prefix should be stripped for wire format
+        assert_eq!(super::strip_routing_prefix("kimi/kimi-k2.5"), "kimi-k2.5");
+        assert_eq!(super::strip_routing_prefix("kimi-k2.5"), "kimi-k2.5"); // no prefix, unchanged
+        assert_eq!(super::strip_routing_prefix("kimi/kimi-k1.5"), "kimi-k1.5");
+    }
 }